CONTRIBUTING.md cleanup

[tomaszmichalak]

Describe the bug We should keep CONTRIBUTING.md details in one place (Knotx/knotx). Please replace the content of:

• https://github.com/Knotx/knotx-dependencies/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-commons/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-launcher/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-server-http/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-fragments/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-template-engine/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-docker/blob/master/CONTRIBUTING.md
• https://github.com/Knotx/knotx-stack/blob/master/CONTRIBUTING.md

UPDATE:

• https://github.com/Knotx/knotx-fragments-chrome-extension/blob/master/CONTRIBUTING.md

with:

![Knot.x logo](http://knotx.io/img/logo-knotx.png)

# How to contribute to Knot.x
Thank you for taking the time to contribute!
We appreciate all commits and improvements, feel free to join Knot.x community and contribute.

Please refer to [CONTRIBUTING.md](https://github.com/Knotx/knotx/blob/master/CONTRIBUTING.md) file for more details.

[tomaszmichalak]

@Skejven Can you please update also: https://github.com/Knotx/knotx-fragments-chrome-extension/blob/master/CONTRIBUTING.md